Wood papers when calendered often appear very irregularly coloured, and the surface looks mottled. Sulphite and mechanical pulps possess very different affinities for aniline dyes, the latter being coloured readily. The dyeing of mixtures of wood-pulps is an art in itself.

Dust from Paper. The dust which gradually accumulates on the type of the printing press may be due to a variety of causes.

In the manufacture of web news the sheet leaving the calenders of the papermachine sometimes rubs against a stationary guide roll before being finally reeled up. The friction causes an accumulation of small fibres and mineral matter at the point of contact, and the accumulated dust comes away periodically with the sheet; when the reel is used at the printing office the dust gives trouble. This defect does not often occur.

The fluff from news is sometimes due to the use of mechanical wood which is coarsely ground. The coarse chips lie on the surface of the sheet and are pressed in by the calender rolls. The friction of the rolls on the printing-machine is sufficient to release many of them and so the type is soon fouled.

Coated papers are a fruitful source of trouble in filling up type and electro blocks. The defect usually arises from an insufficiency of glue in the coating mixture.

Bulky featherweight and antique papers produce fluff on type. The fibres are only loosely felted together in such papers and friction causes the smaller fibrous particles to come away very easily.

Impurities in Paper. This important subject deserves careful attention, because many of the difficulties experienced by printers arise from the presence of impurities in paper. An interesting treatise dealing with specific cases arising during the course of professional practice could be written, and such a book would prove of considerable value. It is impossible to do more than give a brief account of a few actual instances, which the author has had occasion to investigate.

Fibre.-1. One of the most frequent troubles common to newspaper is the breaking of the sheet when passing through the printing machine. With a production of 24,000 copies per hour the loss of time occasioned by an unnecessary break is considerable. In most cases the break may be traced to the presence of coarse fibres or of thin hairs near the edge of the reel, lying at right angles to the direction in which the paper is travelling on the machine. A microscopic examination of the fibre will reveal its nature and determine whether it is a coarse fibre from the pulp or some adventitious substance, such as string.

2. An esparto paper made light and bulky contained some coarse particles which closely resembled mechanical wood when examined with the eye. The microscopic test proved them to be undigested pieces of esparto fibre which by some means had found a lodging-place in the paper.

Acid.-1. Some papers were rejected because they gave an acid reaction with litmus, the extract obtained by treating them with water turning blue litmus papers red. The investigation showed that the papers did not contain any free acid, but merely sulphate of aluminium, which turns blue litmus red. Litmus paper is not a reliable test for free acid.

2. The pages of a novel were found to be disintegrated, the paper crumbling to powder when rubbed between the fingers. This was due to sulphuric acid with which the novel had by some means come into contact. Some of the other pages in the book proved to be normal high-class rag paper.

Particles of dirt.-1. Samples of some common pastings were examined for particles of dirt, many of which fell out of the sheet when the paper was handled, the holes produced causing considerable trouble when the sheet was pasted. The dirt proved to be coarse particles from the china clay used as a loading for the

paper. The clay had not been carefully mixed with water and strained before

use.

2. In some cardboards made by pasting two sheets of paper together some greasy yellowish coloured spots of varying size were found, and at first attributed to faulty paste. Investigation proved this assumption to be incorrect, the defects being due to greasy matter dropping into the pulp on the papermachine.

3. Brownish spots in a photographic mount which were only rendered prominent after pasting were carefully examined, and proved to be minute particles of iron rust, and not a growth of some micro-organism as supposed.

4. Some black specks in a sheet of supercalendered paper were examined and reported as coal. Subsequent inquiries at the mill confirmed this opinion.

Smell.-1. A ream of paper when opened at the warehouse gave off a most unpleasant odour, which gradually disappeared when the sheets were spread out. The smell closely resembled that of sulphuretted hydrogen, and it was found that the paper contained sulphur compounds.

2. Some art paper having an unpleasant odour was found to have been prepared with glue of poor quality.

Mineral matter.-1. A blotting paper of poor quality, which became nonabsorbent after being used a few times, was found to contain lime salts deposited from the hard water with which the rags had come into contact before and after conversion into pulp.

2. A paper guaranteed to have been manufactured without the addition of mineral matter was tested for china clay, which was present to the extent of 2 to 3 per cent. This was eventually traced to the fact that waste papers used in furnishing the beater contained china clay in quantity sufficient to account for the above proportion.

CHAPTER III

ᎡᎪᏀ ᏢᎪ Ꮲ Ꭼ Ꭱ Ꮪ

Preliminary operations.-Sorting, cutting, dusting, boiling, washing-Bleaching-Halfstuff-Beating. Hand-made papers.-Description of process-Tub-sizing-Preparation of animal size-Drying-Plate-glazing. Machine-made papers.-The Fourdrinier

machine

Preliminary Operations.

Rags. The rags used for paper-making consist of a great variety of materials, from new linen and cotton cuttings produced in the factories devoted to the making of wearing apparel, to old, worn and dirty rags which have been discarded from domestic service as useless.

The rags collected by the merchants who supply the paper mill are not mixed indiscriminately, but are properly sorted out into different qualities, so that the paper-maker can obtain the particular grade of raw material best suited to his purpose. Even then the rags are submitted to a second sorting process at the mill, since the quality of the finished paper depends very much upon the condition of the rags. A high-class linen paper cannot be made satisfactorily if the stuff used contains varying proportions of old and worn rags, more or less cotton. The production of a first-rate blotting can only be ensured by a rigid exclusion of all rags except those which experience has proved most suitable. Qualities of Rag. The classification of rags is usually an elaborate process based on certain broad distinctions as to the nature of the fibre, the colour of the The sorting is thus carried out with due regard for

rag and its condition.

1. The Material.

2. The Colour.

The extended nature of the various grades into which the rags are divided both by the merchants for the purpose of sale, and by the paper-maker for manufacture, can easily be gauged by a glance at the market reports of the papertrade press.

Sorting and Cutting. The rags arrive at the mill packed in huge bales, and are then put through a preliminary dusting to remove the greater portion of

any dirt. The duster consists of a long hollow cylinder covered with very coarse wire, inclined at an angle, so that as it revolves the rags thrown in at the upper end travel towards the lower end and discharge themselves free from any loose

dirt.

The rags are then distributed to the various sorting-tables, where buttons, hooks and eyes, leather, rubber and other foreign matter likely to injure the quality of the pulp are carefully removed. The rags are cut by women into long slips, and these again reduced into pieces about four inches square. The cut rags are then finally sorted up and thrown into boxes or baskets placed round

the sorting-table, great care being exercised to keep old and new rags separate, to differentiate the material as to colour and cleanliness, and to preserve uniformity in quality.

Hand-cut rags dealt with in this manner are much more expensive than machine-cut rags, but for high-class paper the latter do not give the best results.

A rag chopper consists of a pair of revolving cylinders carrying one set of

knives which cut the rags into shreds of convenient length, and another set of knives for cutting the shreds into short pieces. There is a greater loss of fibre with machine-cut rags, and the pieces are always very irregular in shape, which is a disadvantage in manufacture. The cut rags are next passed through a dusting-machine known as a " Willow." This machine consists of an iron drum provided with long iron spikes, or teeth, which revolves rapidly inside a closed box, the interior of the latter being provided with similar iron spikes. The rags are thus thoroughly loosened and opened up, the dust and dirt falling through a wire grating below the box. In addition to the drums, the Willow contains a duster similar to that already described, by means of which the rags are completely and finally freed from all impurities of a mechanical nature.

It is estimated that the loss of weight sustained by rags in dusting varies from 1 to 6 per cent., according to quality.

Boiling. The clean rags are next boiled with chemicals to remove fatty and greasy matters, and to dissolve out all substances, such as starch and size, which may be present. The usual process involves the employment of caustic soda, caustic lime, or a mixture of lime with carbonate of soda, which substances are placed in suitable digesters with the rags in definite proportions.

The digesters used are either cylindrical or spherical in shape, 7 to 9 feet in diameter, mounted on suitable trunnions so that they can be rotated slowly. A charge of from two to three tons of rags is thrown into the digester through a man-hole, which is then bolted down. The solution of caustic soda is passed into the boiler through the hollow trunnion and, finally, the steam is admitted through the other trunnion. The conditions under which the rags are boiled vary at different mills, since the factors which determine the process may be altered as required. These factors are: the strength of the liquor, the pressure of steam and the period of boiling. The object of the process is the formation of soluble compounds by the action of caustic soda on the foreign matters in rags, which themselves are insoluble. The soda combines with these to form a soap,